The present invention relates to a convenient means for developing photosensitive materials employing a microencapsulated radiation sensitive composition. More particularly it relates to a photosensitive material of the above type having thermally rupturable microcapsules, wherein the microcapsules are ruptured by the direct application of heat to the photosensitive material following exposure.
Photosensitive materials employing microencapsulated radiation sensitive compositions are the subject of U.S. applications Ser. Nos. 310,356 and 320,643 filed Nov. 12, 1981 assigned to The Mead Corporation and Japanese Laid-Open Application Nos. 57-124343, 57-179836 and 57-197538 to Fugi Photo Film Co., Ltd. In a typical example of the aforementioned photosensitive materials, a color precursor of the electron donor type is encapsulated with a radiation sensitive material and a layer of the microcapsules is coated on a support to provide an imaging sheet. The imaging sheet is image-wise exposed and then assembled with a developer sheet carrying a material which reacts with the color precursor to produce a color image. The assembled sheets are passed together through the nip between two pressure rollers whereupon the microcapsules rupture and image-wise release the color precursor which is transferred to the developer sheet where it reacts and forms an image. In another embodiment, the developer is carried on the imaging sheet in a layer underlying the layer of microcapsules. This sheet is exposed and passed through a pressure nip whereupon the microcapsules rupture and the color precursor migrates to the underlying developer layer where it reacts and forms an image.
The following patents describe other photosensitive imaging materials employing microcapsules:
Berman, U.S. Pat. No. 3,219,446 discloses a transfer imaging process in which a blue-black dye is encapsulated with a photocrosslinkable polymer or a photopolymerizable monomer in a film or a layer of discrete microcapsules. In this system imaging is accomplished by image-wise exposing the layer of the encapsulated material to electromagnetic radiation to crosslink the polymer or polymerize the monomer. This is said to cause the liquid in the exposed microcapsules to assume a non-liquid, rigid condition, such that upon rupturing the microcapsules only the dye from the unexposed microcapsules is transferred to a receiving sheet where images are formed.
Phillips, U.S. Pat. No. 3,700,439, discloses a process wherein Michler's ketone is encapsulated in a conventional manner and provided as a layer on a support. Michler's ketone is not a color former, but irradiation of the ketone converts it to a colorless, acid colorable, dye precursor. Thus, by image-wise exposing the Phillips material to actinic radiation and rupturing the microcapsules in contact with an acid developer layer, such as a layer of acid clay, a visible image is obtained in the areas in which the ketone has been converted to the acid colorable form by irradiation. Phillips also discloses a self-contained system in which the acid developer is on the same support as the microcapsules containing the Michler's ketone.
Levy, U.S. Pat. No. 4,149,887, relates to a microcapsule-containing imaging material having a photoconductive internal phase which is exposed in an RF field. Exposure increases the conductivity of the internal phase and causes the microcapsules to heat, swell and then rupture in the exposed areas thereby freeing the contents to form images. The microcapsules may contain color precursors which form images by reacting with a developing agent.
Japanese Kokai 34488/1977 to Nihon Denshin Denwa Kosha discloses an imaging material in which the microcapsule walls contain a photosensitive material which decomposes and generates a gas upon exposure to actinic radiation. Upon exposure, the capsules rupture and release their internal phase which contains an image-forming agent which reacts with a developer material and produces an image.
Japanese Kokai, 6212/1974 to Matsushita Denki Sangyo K.K., relates to a recording material in which microcapsules having a photocrosslinkable polymer wall contain a colorless or substantially colorless precursor in a polar solvent and, optionally, an acid dye developer. The polar solvent presents the color precursor from reacting with the acid dye developer and forming a color image. Images are formed by image-wise exposing the material to actinic radiation and rupturing the microcapsules in the unexposed areas, whereupon the polar solvent evaporates and color development occurs.
Japanese Kokai Nos., 9519 and 9520/1978 to K. K. Ricoh, relate to imaging systems in which the microcapsules contain a radiation curable internal phase including a dye precursor. Images are formed by image-wise exposing a layer of the microcapsules to light and selectively transferring the microcapsules from the unexposed areas to a receiving sheet. The microcapsules are not ruptured. Upon subsequent wet development processing of the transfer sheet with a dye developer, the dye precursor in the microcapsules is converted to a colored form and an image is obtained.
British Pat. Nos. 1,058,798; 1,141,475; and 1,193,923 to DuPont relate to imaging materials which employ a photopolymerizable substratum comprising a solid binder having a polymerizable ethylenically unsaturated compound dispersed therein. Images are formed by image-wise exposing the materials to actinic radiation. Exposure controls the rate of diffusion of a developer material into or out of the photopolymerizable substratum.
British Pat. No. 1,001,832 to DuPont discloses an imaging material in which a color former may be incorporated in a layer of a photopolymerizable, ethylenically unsaturated compound and an oxygen impermeable cover sheet is placed over the photopolymerizable layer during exposure to limit the concentration of atmospheric oxygen in contact with the photopolymeriable layer and thereby increase the speed and sensitivity of the photopolymerizable material.
Currently, the principal means used to develop photosensitive materials employing microencapsulated radiation sensitive compositions are devices which physically act on the microcapsules to rupture them such as nip rollers and burnishing devices. These devices are costly to manufacture and use, and require frequent maintenance. Thus, there is a need for a less expensive and more efficient means of developing these materials.